The invention relates to a method and apparatus for the protection of electrolysis cells of the mercury cathode type against internal short-circuits which may occur between the anode structure and the liquid mercury cathode (amalgam) due to variations of the amalgam level caused by the accumulation of foreign matter, especially iron particles, or deviations of the amalgam stream caused by corrosion of the cell bottom surface, or malfunction of the mercury recirculation pump.
According to the present invention, whenever the gap between the mercury cathode and the anodes is decreased below a safety limit in correspondence of any region of the active surface, and the local current intensity thereby reaches a dangerous level, an electromechanical system (motorized device) controlled by a computer processing voltage and current data is provided to carry out the automated raising of one or more anode rows. Moreover, in order to minimize the energy consumption directly related to the interelectrodic gap, the electromechanical system of the invention, controlled by a computer processing voltage and current data, will provide for lowering of one or more anode rows to restore the interelectrodic gap at a minimum pre-established safety level.
In a typical horizontal cathode mercury cell of the type illustrated, for example, in FIGS. 1 and 2, several types of anode adjusting devices have been applied in the past such as those herein described:
MULTIPLE LEVERS: this system, also called xe2x80x9cgull wingsxe2x80x9d type, is a fully movable apparatus consisting in a rectangular frame and three double levers, one along the longitudinal axis and two along the transversal axis of the cell, each lever being equipped with two arms. In this case, the movement of the frame is a combination of the shifting of both longitudinal and transversal lever systems. Such apparatus is complex, expensive and suitable only for large-size frames supporting three or four anode rows moving all together, with a consequently low efficiency in energy saving as localized gap control is not made possible.
FOUR JACKSCREWS: this system consists in a frame equipped with four jackscrews positioned at the corners of the frame and two gear motors each driving two jackscrews. Also in this case the system, due to the cost, is conveniently applied only to large size frames bearing three or four anode rows and consequently is a low efficiency system as above explained.
TORSION BAR: this system consists in a rectangular frame with two shafts assembled under the two shorter sides. The two shafts are rotated by means of a gear motor acting, by means of a worms crew, on two arms each connected to one shaft. Having each shaft two plates welded at the ends bearing on four supporting columns, as the shafts rotate a shifting of the entire apparatus is originated. This system cannot guarantee a very precise control of the lifting velocity.
PINIONS AND CHAINS: this system comprises a frame secured to four threaded rods and vertically shifted by means of four pinions rotating thereon, all connected by a chain, one of which being powered by a gear motor. This system cannot allow the necessary precision of the movements due to the loosening and wearing of the chains in time.
It is an object of the present invention to provide a motorized device suitable for adjusting the anodes so as to prevent short-circuits in mercury cathode electrolytic cells as well as to break eventual short-circuits before damaging of the anode structures occurs.
It is another object of the invention to substantially reduce the energy consumption directly related to the extent of the interelectrodic gap, providing means for adjusting the distance of one or more anode rows from the liquid mercury cathode in order to bring the interelectrodic gap down to a minimum pre-determined safety level.
It is another object of the invention to overcome the drawbacks of the above described systems of the prior art, providing a new motorized device suitable for adjusting the anodes, having following main features and advantages:
low cost
simplified and strong mechanical structure
precision of shifting
optimized shifting velocity
easier assembly
single anode row shifting
It is another object of the present invention to provide a motorized device suitable for adjusting the anodes with an optimized interelectrodic gap control efficiency by means of the possibility of single anode row shifting and of the easy computer controlled operation on the basis of current and voltage measurements.